Various applications require the installation of underground pipes between two stations, such as between two manholes or the two sides of a highway, without creating a trench between them.
Several prior techniques have been developed to accomplish trenchless installation of carrier pipes (also known as product pipes) or protective tubular casings (normally steel casings). Most of these methods are based on a static pushing force applied to the pipe against the ground; that is, pipes or casings are jacked through the ground by means of a hydraulically operated jacking unit from a previously prepared starting or entry shaft to a target shaft. In general, all of these pipe jacking-based installations (e.g., horizontal auger boring machines, guided boring machines, and micro-tunneling machines, among others) require a rotating shield or cutting head at the front of the first pipe, in order to cut the ground in front of it, as well as a system to transport the spoils to the starting pit. Moreover, all these methods have in common the need for large and powerful hydraulic jacks to overcome not only the skin friction of the pipes being installed, but also an extra penetration force in order to be able to cut the ground in front of the cutting head.
One case of an auger boring machine is presented in U.S. Pat. No. 4,013,134 (see FIG. 1). In general, the machine 100 comprises a base 101 that includes spaced track members, which are disposed in a trench adjacent to the hill to be bored. The machine also includes a frame mounted for movement along the track means 102, and such carriage 103 supports a power train for rotating connected sections of auger shafts 104, which comprise a progressively extendable boring auger. The frame supports a pusher ring 105 for driving sections of casings into the bored hole, and an associated pushing cylinder is provided for advancing and retracting the frame and pusher ring along the track.
One disadvantage of this type of machine relies on the need for a complete set of augers (at least same length of the total drive) with a similar diameter of the pipe to be installed in order to drag the soil coming from the cutting head to the jacking pit or entry shaft. Therefore, if a different project requires the installation of pipes of a different diameter, in most of the cases, the whole auger set has to be purchased again. Another disadvantage of using a continuous auger is the high torque requirements of this type of system. The high torque increases the chances of injury or death for people working close to the machine since there is a risk that the machine will flip on its side when facing tough grounds, smashing anything or anyone close to it. The high torque requirements are a consequence of the torque needing to cut the natural ground in front of the cutting head, the energy required to move the whole set of augers inside the steel casings, and/or the torque needed to drag the spoils along all the installed pipes. This continuous auger-based spoil extraction system produces the drag of spoils as a reaction produced by the spinning of those augers surrounded by the dirt. In this process, a considerable part of the energy is lost by friction and by the radial force component resulting between the ground and the augers. Another issue with this method is that, in shallow installations or sandy soils, there is a risk of generating a sinkhole.
Other trenchless methods are related to micro-tunneling machines. Such systems involve a whole family of machines with some variations among them. Many of the variations differ on how the soil is excavated and how the spoils are transported to the surface of the jacking shaft. In general terms, they include a boring shield that is pushed forward by the product pipes behind it, which are being jacked by large and robust hydraulic jacks in the launch pit. As these micro-tunnel boring machines move forward through the ground, the soil is removed by typically mixing it with a fluid, to then pump the mixture out of the tunnel into a separation plant, wherein the solids are separated from the fluids. An alternative way to transport the excavated soil is by the means of a short auger located just behind of the cutting shield, filling bucket carts that are continuously moving back and forward inside the tunnel, and carrying out the excavated material. These methods do not always work well in shallow applications, depending on soil type. In addition, tunnel boring tends to be slow and expensive because of the type of equipment required, and because the cutting shield is specially manufactured or selected based on the specifications of each project (e.g., a diameter of the pipe and ground conditions).
Alternatively, other methods are based on percussive impacts for ramming steel pipes into the ground rather than using static jacking forces. In most of these cases, these steel pipes mostly are protective pipes for accommodating the final carrier pipes inside of them. Normally, these impact-based methods have an open-end cutting edge at the front of the first pipe to let the ground coming in. Once the installation is completed, a procedure starts to mechanically, hydraulically, pneumatically or manually extract the ground inside the pipe. One example of an impact-based method is the Paul Schmidt, U.S. Pat. No. 4,671,703 (e.g., as shown in FIG. 2)
In one conventional approach to pipe ramming 200, a percussive pneumatic hammer 201 is used to drive the pipe 202 horizontally or at an angle into the ground. The hammer's housing is attached to the end of the pipe by means of a suitable fitting 203 and is sometimes further secured by cables. A piston-actuated ram strikes a plate inside the housing and the percussive force is transmitted to the end of the pipe through the housing, thereby causing the pipe to advance into the ground. Pneumatic rammers are characterized by producing several blows per minute, delivering low to medium energy on each blow. A typical small pneumatic hammer offers 0.17 kJ of energy and delivers 580 blows per minute, weighing less than 10 kg. A typical large hammer has 40 kJ of energy, weighs 12 metric tons and delivers 180 blows per minute.
Hydraulic (rather than pneumatic) hammers are often used in vertical drilling. This type of large hammers generally operates at fewer strokes per minute but delivers much more per blow. In this case, the strike piston extends outside the hammer housing to strike the casing. Typically, one hydraulic hammer weighs 4 metric tons, delivers 65 blows per minute at 30 kJ, while a 242 metric ton hammer delivers 2300 kJ at 30 blows per minute. In vertical drilling, the hammer housing is maintained in contact against the casing principally by means of gravity. Even if they are not commonly used for horizontal pipe ramming, they are an alternative when installing large casing diameters. However, because the ram extends outside the hammer housing, it is not practical to secure the housing to the pipe. It therefore becomes essential to provide crowd of the hammer against the pipe. One approach 300 to doing so is disclosed by Verkyk, U.S. Pat. No. 6,652,190, which relies on a cable winch crowd system 301 (see, e.g., FIG. 3A).
A recent improvement 302 of the Verkyk invention is disclosed by U.S. Patent Pub. No. 2016/0333642 to Bachand et al, in which the winch-based crowd is substituted by a carriage that is urged forward by hydraulic cylinders acting between the carriage and an abutment (see, e.g., FIG. 3B). A compressive resilient assembly is mounted on the carriage 303 in order to release its energy to the hydraulic hammer 304 to keep it in contact with the pipe 305 after each impact. Since this technology employs a hydraulic hammer, the space requirements for the entry pit will be considerably larger than the space needed for other trenchless techniques, making this machine suitable mostly to large diameter installations (e.g., pipes over 72 inches in diameter), like in the case of its predecessor (Verkyk, U.S. Pat. No. 6,652,190). Another deficiency of the Bachand publication is that the penetration is essentially generated by the hammer's impacts. In such a case, the hydraulic force is used to keep the large hydraulic hammer in place (attached to the pipe) and not to counteract the natural pipe elasticity or to notably increase the penetration force. Furthermore, due to the high-energy impact peaks generated by the hydraulic hammer, it is impractical to apply high static force to the pipe since this will lead to the use of considerable thicker steel casings to avoid damages in the pipe.
Regardless the type of rammer used, one common problem with percussive pipe ramming methods (including Bachand) is that the soil-clearing process cannot be done at the same time with the installation process, leading to a reduction in overall productivity. Another common problem is the need of relatively high energy quantities (big hammers) to install the pipes or casings since a considerable part of the energy of each impact is lost. One relevant part of the energy is absorbed by the natural steel pipe elasticity, and the pipe's external and internal skin friction (from the soil coming inside) dissipates another important part of the energy. Additionally, due to the momentum transferred from the rammer to the pipe, the extra mass added to the pipe due to the soil coming inside it during operation diminishes the acceleration of the cutting edge, reducing the penetration force in the front of the first pipe. All of these undesired effects are magnified as the length of the drive increases, limiting this method to be useful only for relatively for short drives (normally less than 300 feet).
Furthermore, all of the above trenchless methods have their own limitations and applicability depending on the length, diameter, precision requirements and ground conditions. Moreover, all these machines are designed to overcome the maximum length and diameter in which they were preconceived, even if that means to be overpowered for shorter drives or smaller diameters. Finally, most of the machines listed above (especially pipe jacking-based methods) have their main parts specifically dimensioned for a specific pipe diameter, and every time a new diameter has to be installed, a significant investment has to be made in a new custom part.